Resonance trapping, stochastic diffusion and incoherent emittance growth induced by structured electron-cloud pinch

When a bunch passes through an electron cloud, the transverse electron density distribution is enhanced and modulated in time as a consequence of the motion of individual electrons under the action of the nonlinear beam field. The effect of this “structured” electron pinch together with the synchrotron motion of beam particles leads to an incoherent emittance growth via the excitation and repeated crossing of resonances, that can give rise to either stochastic “scattering” (“diffusion”) or trapping. We study these effects via a toy model of an idealized pinch, and present applications to the CERN SPS and the GSI SIS100

Electron-Cloud Intrabunch Density Modulation

During the passage of a proton bunch through an electron cloud, a complicated electron density modulation arises, with characteristic ring or stripe patterns that move radially outward along the bunch. We present simulation results for field-free and dipole regions, which reveal the morphology and main features of this phenomenon, explain the physical origin of the stripes in either case, and discuss the dependence on key parameters

Analysis of resonancesinduced by the SIS-18 electron cooler

Besides beam cooling, an electron cooler also acts as a non-linear optical element. This may lead to the excitation of resonances possibly resulting in an increase of the beam emittance. The aim of this work is the calculation of resonances driven by the electron space charge field in the cooler installed in the SIS heavy ion synchrotron at GSI Darmstadt. For our calculations, we used a numerical model consisting of a rotation matrix representing the ideal lattice together with a non-linear transverse kick element representing the electron cooler. Within this model, we studied the dominant resonance lines resulting from the interaction with the cooler